The present invention generally relates to manufacturing of large scale structures using composite materials and, more particularly, to automated composite lamination of large aircraft fuselage sections.
The structural performance advantages of composites, such as carbon fiber epoxy and graphite bismaleimide (BMI) materials, are widely known in the aerospace industry. Aircraft designers have been attracted to composites because of their superior stiffness, strength, and lower weight, for example. As more advanced materials and a wider variety of material forms have become available, aerospace usage of composites has increased. Automated tape layer technology has developed to become a widely used automated process for fabrication of large composite structures such as wing panels and empennage. Current tape layer technology has been improved to offer flexibility in process capabilities required for a wide variety of aerospace components. As aerospace industry tape laying applications achieve material lay up rates, for example, that may help control the manufacturing cost of large composite structures, new and innovative applications for tape layers may be defined, such as the automated tape lay up of large aircraft fuselage sections, for example, 15 to 20 feet in diameter.
Automated tape laying machines typically are gantry style machines that may have, for example, ten axes of movement with 5-axis movement on the gantry and 5-axis movement on the delivery head. A typical automated tape layer consists of a gantry structure (parallel rails), a cross-feed bar that moves on precision ground ways, a ram bar that raises and lowers the material delivery head, and the material delivery head which is attached to the lower end of the ram bar. Commercial tape layers are generally configured specifically for lay up of flat or mildly contoured laminate applications using either flat tape laying machines (FTLM) or contour tape laying machines (CTLM). On a gantry style tape layer, tooling (or a flat table) is commonly rolled under the gantry structure, secured to the floor, and the machine delivery head is then initialized to the lay up surface.
FIG. 1A provides an illustration of a typical tape laying machine material delivery head 100. Delivery heads for FTLM and CTLM machines are basically the same configuration as that of delivery head 100 shown in FIG. 1A. The delivery heads on commercial automated tape layers are typically configured to accept material widths of 75 mm (3 inches), 150 mm (6 inches), and 300 mm (12 inches). Flat tape layers typically use material in 150 mm (6 inch) and 300 mm (12 inch) widths. Contour tape layers typically use material in 75 mm (3 inch) and 150 mm (6 inch) widths. CTLM systems normally use the 3-inch or 6-inch wide material when laying up off flat plane contour surfaces. Material 102 for tape layers generally comes in large diameter spools. The tape material 102 has a backing paper 106, which must be extracted as the prepreg (resin pre-impregnated fiber) is applied to the tool surface 108. The spool of material typically is loaded into the delivery head supply reel 104 and threaded through the upper tape guide chute and past the cutters 110. The material 102 then passes through the lower tape guides, under the segmented compaction shoe 112, and onto a backing paper take up reel 114. The backing paper is extracted and wound on a take up roller of paper take up reel 114. The delivery head 100 makes contact with the tool surface 108 and the tape material 102 is “placed” onto the tool surface 108 with compaction pressure. The tape laying machine typically lays tape on the tool surface 108 in a computer programmed path (course), cuts the material 102 at a precise location and angle, lays out tail, lifts delivery head 100 off the tool surface 108, retracts to the course start position, and begins laying the next course. The delivery head 100 may have an optical tape flaw detection system that signals the machine control to stop laying tape material 102 when a flaw has been detected. The delivery head 100 also typically has a heating system 116 that heats the prepreg materials to increase tack levels for tape-to-tape adhesion. Heated tape temperatures generally range from 80 F. to 110 F.
While CTLM delivery heads handle a single piece of wide prepreg tape, fiber placement heads process multiple strips of narrow tape to form a solid band of material similar to tape. Individual prepreg fibers, called tows, are typically one eighth inch wide. Tows 118 are shown in FIGS. 1B, 1C, and 1D. Tows 118 usually are pulled off spools—such as towpreg spool 120—and fed through a fiber delivery system 122 into a fiber placement head 130, which is shown schematically in FIG. 1C. Fiber delivery system 122 may include, for example, a tensioner system 124.
In the fiber placement head 130, tows 118 may be collimated into a single fiber band 126, as shown in FIG. 1B, and laminated onto a work surface, such as surface 140, which can be mounted between a headstock and tailstock. When starting a fiber band or course, such as course 128 shown in FIG. 1D, the individual tows 118 are fed through the head 130 by releasing the clamps 139 and simultaneously activating the pinch rollers 132 against rotating add rollers 134. While the material is being placed, it is usually compacted onto a surface—such as surface 140 with a compaction roller 136. The pinch rollers are retracted once the tows are fed under the compaction roller, allowing each tow to pay out through the head as required by the path along the tool. As the course 128 is being laid down, the head 130 can cut or restart any of the individual tows 118. FIG. 1C shows a cross section schematic of the mechanisms in the fiber placement head 130 for an upper 119a and lower 119b fiber path 119. Each tow path 119 has its own cutter 138, pinch roller 132, and clamp 139 that can be actuated independently from all the other tow paths 119. This permits the width of the fiber band 126, or course 128, to be increased or decreased in increments equal to one tow width as shown in FIG. 1D. Adjusting the width of the fiber band 126, or course 128, eliminates excessive gaps or overlaps between adjacent courses 128. At the end of the course 128, the remaining tows 118 may be cut to match the shape of the ply boundary 142. When the tows are cut, the clamps 39 are simultaneously actuated to prevent it from slipping or being pulled out of the head by the tension. The head 130 may then be positioned to the beginning of the next course 128. During the placement of a course 128, each tow 118 is dispensed at its own speed as determined by the machine path along the tool surface, allowing each tow 118 to independently conform to the surface 140 of the part. Because of this, the fibers, i.e., tows 118, are not restricted to geodesic paths. They can be steered to meet specified design goals. A rolling compaction device, such as compaction roller 136, combined with heat for tack enhancement, laminates the tows 118 onto the lay-up surface 140. This action of pressing tows 118 onto the work surface 140 (or a previously laid ply) adheres the tows 118 to the lay-up surface 140 and removes trapped air, minimizing the need for vacuum debulking. It also allows the fiber to be laid onto concave surfaces.
A fiber placement head 130, like the tape laying head 100, may be provided with several axes of motion, using an arm mechanism, for example, and may be computer numeric controlled. The axes of motion may be necessary to make sure the head 100 or 130 is normal to the surface 108 or 140 as the machine is laminating tows. The machine may also have a number of electronic fiber tensioners, such as tensioner system 124, which may be mounted, for example, in an air conditioned creel. These tensioners may provide individual tow payout and maintain a precise tension. The head 100 or 130 may precisely dispense, cut, clamp, and restart individual prepreg tows 118.
Fuselage fabrication using composites requires automated placement of composite materials at a rate high enough to make the use of composites economical compared to conventional methods of fuselage fabrication. To take advantage of the light weight and high strength of composite materials for newer, larger fuselages to be built will require a break through increase in composite material lay down rates. Current processes such as tape laying and fiber placement are currently too slow to be economically viable to meet production rates on new large scale aircraft programs, such as Boeing's 7E7. Tools and processes for automated placement of composite materials are needed that greatly increase the lay down rates over the state of the art, and which will reduce the number of machines required.
For example, an entire large fuselage skin of constant cross section 60 feet long would typically require three to four weeks to be placed onto a lay-up mandrel using existing technology. Where standard automated lamination processes can place material up to 20 pounds per hour (lbs/hr) sustained, an automated composite placement machine is needed that can approach on the order of 1,000 lbs/hr so that an entire large fuselage skin of constant cross section, which typically may be 60 feet long but can range in length, for example, from about 20 feet to about 110 feet or longer, can be placed onto a lay-up mandrel in a day or two. The reduction in time can significantly increase the practicality and economic viability of manufacturing large aircraft parts, such as large fuselage skins, using composite materials.
As can be seen, there is a need for an automated lay-up machine for composite fabrication of large fuselage sections. There is also a need for fabrication of composite parts using an automated lay up machine and process that greatly increases the lay down rates over the state of the art. Moreover, there is a need for an automated lay up machine and process that will reduce the number of machines that are required, reducing the required factory space and overall capital investment needed.